Formal charge is the apparent electronic charge of each atom in a molecule based on the electron dot structure. Formal charge can be used to help in the assessment of resonance structure. Charge on the molecule or ion is equal to sum of all the formal charges. 

X= Number of valence electrons in a free atom 
Y= Number of unshared electrons on the atom 
Z= Number of bonds on the atom 
Formal charge = (X) -(Y)-(Z))

Find formal charge on sulphur and nitrogen atom in :

• A

  -1 and zero

• B

  -I and -1 

• C

  +1 and-2

• D

  +1 and zero

Which of the following is +1 in ${\mathrm{NO}}_3^{-}$ ion? 

• A

  Sum of all formal charges

• B

  Formal charge on single bonded oxygen

• C

  Formal charge on nitrogen

• D

  Average formal charge on oxygen

What is the formal charge (average) on oxygen in ${\mathrm{CO}}_3^{2-}$? 

• A

  -2 

• B

  -2.5

• C

  -0.67

• D

  Zero 

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